Telecommunications systems are carrying increasing amounts of information, both in the long distance network as well as in metropolitan and local area networks. At present data traffic is growing much faster than voice traffic, and will include high bandwidth video signals. In addition to the requirement for equipment to carry increasing amounts of telecommunications traffic there is a need to bring this information from the long distance network to businesses and to locations where it can be distributed to residences over access networks.
The equipment which has been developed to carry large amounts of telecommunications traffic includes fiber optic transport equipment which can carry high speed telecommunications traffic. The data rates on fiber optic systems can range from millions of bits per second (Mb/s) to billions of bits per second (Gb/s). In addition, multiple wavelengths of light can be carried on an optical fiber using Wavelength Division Multiplexing (WDM) techniques.
The ability to carry large amounts of telecommunications traffic on an optical fiber solves the long-distance point-to-point transport problem, but does not address the issue of how to add and remove traffic from the high-speed data stream. Equipment for adding and removing traffic has been developed and is referred to as xe2x80x9cadd-dropxe2x80x9d multiplexing equipment.
Traditional designs for add-drop multiplexers are based on the use of multiple interface cards which receive high speed data streams, create a time division multiplex signal containing the multiple data streams, and route the time division multiplex signal to a cross-connect unit which can disassemble the data streams, remove or insert particular data streams, and send the signal to another interface card for transmission back into the networks. By aggregating the multiple data streams into a time division multiplexed data signal, the data rate of the time division multiplexed signal is by definition several times the rate of the maximum data rate supported by the interface cards. Such solutions have proven adequate for interface data rates in the range of 155 Mb/s to 622 Mb/s, but for data rates over 1 Gb/s there are a number of problems which arise due to the transport of and timing of the multiplexing and transmission of the high speed signals between cards in the cross-connect. Optical signals of 2.4 Gb/s have become a standard and there is a need for cross-connect equipment which can support multiple 2.4 Gb/s data streams.
Standardized interfaces and transmission hierarchies for telecommunications signals have been developed and include the pleisochronous digital hierarchy (PDH) standards, the Synchronous Digital Hierarchy (SDH) standards, and the Synchronous Optical Network (SONET) standards. In addition to these telecommunications transport standards and systems data standards and systems have been developed for interconnecting businesses and computers within businesses. These metropolitan and local area network (MAN/LAN) standards include Ethernet, Gigabit Ethernet, Frame Relay, and Fiber Distributed Data Interface (FDDI). Other standards, such as Integrated Services Digital Network (ISDN) and Asynchronous Transfer Mode (ATM) have been developed for use at both levels. Although individual pieces of equipment can be purchased to support telecommunications or MAN/LAN standards, these devices generally either connect data streams using a signal protocol or convert entire data streams from one protocol to another. There is a need for a device which can establish interconnectivity between interfaces at the MAN/LAN level, while providing cross-connection to the telecommunications PDH/SDH/SONET network.
Multiple interfaces are presently supported in cross-connect equipment by the use of different interface cards. For high-speed signals, these cards must be inserted into particular slots in order to insure that the signal can be transported between the interface card and the cross-connect unit and to another interface card. It would be desirable to have a cross-connect system in which cards can support high-speed optical signals of at least 2.4 Gb/s in any card slot.
It would also be useful to have a system which would support routing, bridging, and concentration functions within MANs/LANs, as well as permitting access to the telecommunications PDH/SDH/SONET network.
Because of the high data rates and amount of traffic carried in the telecommunications signals, it is necessary to insure that there are redundant interface units in the cross-connect, and that a protect interface card can be used if a working interface card fails.
For the foregoing reasons, there is a need for flexible cross-connect with a data plane that can support multiple high speed optical interfaces in any card slot, can establish connectivity between data cards and the transport network and which provides adequate protection against failed units.
The present invention provides a flexible cross-connect architecture with a data plane based on use of interface cards which are inserted into card slots connecting to a backplane which provides point-to-point connectivity between each card and centralized cross-connect and timing, communications, and control units. The cross-connect unit can establish connections between any interface card and any other interface card, or between an interface card and itself.
A star backplane is utilized in which point-to-point connections are established between network interface cards and common cards including a cross-connect card and redundant cross-connect card, and a timing, communications and control card and redundant timing, communications and control card. In addition, the star backplane supports point-to-point connections between the network interface cards, allowing the creation of a data plane which does not require use of the cross-connect to route data.
In a preferred embodiment the interface cards support a variety of data and telecommunications interfaces including SONET OC-192 interfaces operating at 9.95 Gb/s. The point-to-point connections between the interface cards and the cross-connect operate over a parallel 32 bit data bus, operating at 311 MHz and supporting transport of STS-192 payloads. In an alternate embodiment a limited number of card slots support STS-192 data rate connections to the cross-connect, while all of the card slots support STS-48 connections to the cross-connect.
The present invention utilizes a backplane which supports direct connections between interface cards, allowing for the creation of a data plane in the form of a fully or partially connected mesh. One advantage of the data plane is that signals can be routed between interface cards without use of the cross-connect in order to realize bridging, routing, and other MAN/LAN functions without encumbering the cross-connect.
Another advantage of the data plane is that traffic signals can be aggregated in the data plane and routed to the telecommunications network. As an example, Ethernet data can be aggregated on one or more interface cards which form part of the data plane. The aggregated traffic can be used to fill a DS-3, STS-1 or other signal which forms part of a SONET channel. The cross-connect can insert the aggregated signal into a higher level SONET signal for transport on the telecommunications network. This feature allows for the cost effective use of the equipment and alleviates the need for a customer to lease an expensive high speed optical signal for a limited amount of data traffic.
The present invention supports a cross-connect unit, a control unit, a plurality of interface cards, and has a plurality of interface card slots which are connected to a backplane. The backplane establishes point-to-point connections between the interface cards and the control unit and between the interface cards and the cross-connect such that any signal from an interface unit can be cross-connect with a signal from another interface unit, independent of the slots in which the interface units are located.
In a preferred embodiment a variety of interface cards are used to support electrical connections including Ethernet, ATM, PDH and SDH rates, as well as optical connections at rates up to STS-192. In a preferred embodiment any interface card can be located in any interface card slot and signals from a card can be cross-connected with any other signal including a signal from that card itself.
In an alternate embodiment optical connections of up to OC-48 are supported in any interface card slot, and optical connections of OC-192 are supported in particular slots.
An advantage of the present invention is that multiple SONET rings can be supported from one piece of equipment, since cross-connections can be established between separate rings at the cross-connect.
In a preferred embodiment cross-connection is performed at high speed by pre-aligning signals on the interface cards to create a frame aligned signal which arrives at the cross-connect. Pre-aligning the signal can be accomplished through the use of a programmable offset located on each interface card and controlled by a central timing, communications, and control unit.
A feature of the present invention is the ability of the cross-connect to break the signal down to its lowest common denominator to subsequently perform the cross connection. In a preferred embodiment the cross-connection is done at a VT 1.5 level while in an alternate embodiment the cross connection is performed at the STS-1 level.
A feature of the present invention is the ability to protect against failed interface cards (electrical protection). In a preferred embodiment this is accomplished by establishing connections on the backplane which connect each card with an outwardly adjacent card, as well as providing connectivity to a designated protect card. Traces are established on the backplane which permit the system to be configured for 1:1, 1:5 or simultaneous 1:2, 1:1, 1:N, and unprotected protection schemes on each side of the cross-connect. The timing, communications, and control unit can be utilized to monitor for failed devices and control use of a protect card.
An advantage of the present invention is that protect cards can be used to carry traffic when not being used by the working card. Another advantage of the present invention is the ability to change the working:protect ratio without modification of cards or the backplane.
These and other features and objects of the invention will be more fully understood from the following detailed description of the preferred embodiments which should be read in light of the accompanying drawings.